330d6fd063
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@4359 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
87 lines
4.5 KiB
TeX
87 lines
4.5 KiB
TeX
\section{Drag-and-drop and clipboard overview}\label{wxdndoverview}
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Classes: \helpref{wxDataObject}{wxdataobject},
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\helpref{wxTextDataObject}{wxtextdataobject},
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\helpref{wxDropSource}{wxdropsource},
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\helpref{wxDropTarget}{wxdroptarget},
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\helpref{wxTextDropTarget}{wxtextdroptarget},
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\helpref{wxFileDropTarget}{wxfiledroptarget}
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Note that wxUSE\_DRAG\_AND\_DROP must be defined in setup.h in order
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to use Drag'n'Drop in wxWindows.
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This overview describes wxWindows support for drag and drop and clipboard
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operations. Both of these topics are discussed here because, in fact, they're
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quite related. Drag and drop and clipboard are just two ways of passing the
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data around and so the code required to implement both types of the operations
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is almost the same.
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Both operations involve passing some data from one program to another,
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although the data can be received in the same program as the source. In the case
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of clipboard transfer, the data is first placed on the clipboard and then
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pasted into the destination program, while for a drag-and-drop operation the
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data object is not stored anywhere but is created when the user starts
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dragging and is destroyed as soon as he ends it, whether the operation was
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ended successfully or cancelled.
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To be a {\it drag source}, i.e. to provide the data which may be dragged by
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user elsewhere, you should implement the following steps:
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\begin{itemize}\itemsep=0pt
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\item {\bf Preparation:} First of all, the data object must be created and
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initialized with the data you wish to drag. For example:
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\begin{verbatim}
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wxDataObject *my_data = new wxTextDataObject data("This string will be dragged.");
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\end{verbatim}
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\item{\bf Drag start:} To start dragging process (typically in response to a
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mouse click) you must call \helpref{DoDragDrop}{wxdropsourcedodragdrop} function
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of wxDropSource object which should be constructed like this:
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\begin{verbatim}
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wxDropSource dragSource( this );
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dragSource.SetData( my_data );
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\end{verbatim}
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\item {\bf Dragging:} The call to DoDragDrop() blocks until the user release the
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mouse button (unless you override \helpref{GiveFeedback}{wxdropsourcegivefeedback} function
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to do something special). When the mouse moves in a window of a program which understands the
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same drag-and-drop protocol (any program under Windows or any program supporting the
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XDnD protocol under X Windows), the corresponding \helpref{wxDropTarget}{wxdroptarget} methods
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are called - see below.
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\item {\bf Processing the result:} DoDragDrop() returns an {\it effect code} which
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is one of the values of \helpref{wxDragResult}{wxdropsource} enum. Codes
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of wxDragError, wxDragNone and wxDragCancel have the obvious meaning and mean
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that there is nothing to do on the sending end (except of possibly logging the
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error in the first case). wxDragCopy means that the data has been successfully
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copied and doesn't require any specific actions neither. But wxDragMove is
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special because it means that the data must be deleted from where it was
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copied. If it doesn't make sense (dragging selected text from a read-only
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file) you should pass FALSE as parameter to DoDragDrop() in the previous step.
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\end{itemize}
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To be a {\it drop target}, i.e. to receive the data dropped by user you should
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follow the instructions below:
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\begin{itemize}\itemsep=0pt
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\item {\bf Initialization:} For a window to be drop target, it needs to have
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an associated \helpref{wxDropTarget}{wxdroptarget} object. Normally, you will
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call \helpref{wxWindow::SetDropTarget}{wxwindowsetdroptarget} during window
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creation associating you drop target with it. You must derive a class from
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wxDropTarget and override its pure virtual methods. Alternatively, you may
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derive from \helpref{wxTextDropTarget}{wxtextdroptarget} or
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\helpref{wxFileDropTarget}{wxfiledroptarget} and override their OnDropText()
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or OnDropFiles() method.
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\item {\bf Drop:} When the user releases the mouse over a window, wxWindows
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queries the associated wxDropTarget object if it accepts the data. For this,
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a \helpref{wxDataObject}{wxdataobject} must be associated with the drop target
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and this data object will be responsible for the format negotiation between
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the drag source and the drop target. If all goes well, then \helpref{OnData}{wxdroptargetondata}
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will get called and the wxDataObject belonging to the drop target can get
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filled with data.
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\item {\bf The end:} After processing the data, DoDragDrop() returns either
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wxDragCopy or wxDragMove depending on the state of the keys (<Ctrl>, <Shift>
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and <Alt>) at the moment of drop. There is currently no way for the drop
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target to change this return code.
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\end{itemize}
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